Embodiments of the present invention relate to electrochemical sensors, and more particularly, to a sensing circuit for an electrochemical sensor.
High end sensors for measuring a hydrogen concentration, or a pH value, of a fluid, in which the sensor is submerged have existed for some time. However, effective digital measurement using such devices can be challenging. For example, typical probes used on a pH circuit generate voltages on the order of a few millivolts to several hundred millivolts. Such probes can also generate negative voltages which are problematic because, most analog to digital converters (ADCs) used to perform most digital measurements, are not equipped to measure negative voltages. As such, for effective digital measurement, a system's analog front end (AFE) should be designed to not present the ADC with a negative voltage. Through signal conditioning, it is also desirable for the system to use most, if not all, of the dynamic range of the ADC, as well as filter and/or suppress noise presented to the ADC.
To ensure the dynamic range of the ADC is most effectively used, typical circuits will introduce gain in the AFE section of the circuit. This typically presents several problems, such as a) the gain introduces noise, b) the gain introduces other error (e.g., input offset current gain and other gain nonlinearities), and c) the gain must be variable to effectively condition a wide variety of signals.
It is therefore desirable to provide a sensing circuit for an electrochemical sensor that enables use of most of the dynamic range of the ADC, increases sensitivity and accuracy, and provides data in a digital form that can be transferred and utilized by further systems.